In the treatment of wastewater, it is generally desirable to remove water content through dewatering, inactivate pathogenic micro-organisms, spore, and helminth, remove/deposit heavy metals, remove/change or decrease endocrine disrupting compounds, and/or remove other undesirable compounds which may be organic or inorganic.
The dewatering process removes water, increases the concentration of solids, and reduces volume, thus reducing the costs of further treatment and handling. Dewatering in practice is accomplished through natural (e.g. evaporation, gravity, etc.) and mechanical methods. The most often used mechanical dewatering devices include centrifuges, belt filter presses, screw presses, etc. All of these commonly used dewatering techniques however do not improve the chemical composition of biosolids and pathogen removal is typically done separately and requires a long time. Dewatering does not remove metals or pathogens and converts sludge slurry to a cake of approx 20-30% Total Solids (TS).
Inactivation is performed infrequently, though there is a growing emphasis on Class A biosolids sent to agriculture. Class A means (according to US EPA) biosolids can be beneficially utilized without any restrictions. Typical inactivation may include addition of chemicals (oxidation agents, acids or lime); heat treatment (70 to 150° C.); thermophilic digestion; heat drying. In most cases target pathogen-indicators are fecal coliforms (FC) or total coliforms (TC); very rarely Salmonella content is checked. Viruses, Clostridium p. or helminth ova (eg. Ascaris) are often used as indicators of the efficiency of disinfection.
Heavy metals are not known to be removed at all in any prior art wastewater treatment. Biosolids containing excessive heavy metals cannot be utilized and must be disposed in landfill. Sludge disposal in landfills is not permitted in Europe and getting to be so in America.
Furthermore, Endocrine Disrupting Compounds (EDC) removal is not accomplished on purpose in the conventional biosolids processes. It is anticipated that regulators will want EDC removed before land application.
One known process for simultaneous dewatering and pathogen inactivation involves applying potential gradients to sludge to be treated in the presence of a liquid conditioner. Removal of metals however must be accomplished in a separate process in the prior art.